According to The Wall Street Journal, citing officials at Apple's suppliers, the company is testing smartphone screens larger than the 4-inch version on the iPhone 5. They're also exploring tablet screens measuring just under 13 inches.

The report says it's not clear when -- or even if -- these larger screens might be featured on future devices.

Several smartphone and tablet makers, most noticeably Samsung, have shifted toward larger screens for its devices. Samsung's Galaxy Note lineup of smartphones has been surprisingly popular since launching in October 2011. Last August, the company revealed the Galaxy Note topped 10 million sold.